This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to increase understanding regarding the genetic underpinnings of psychiatric illness and chronic pain- conditions that are common in individuals exposed to combat. To accomplish this, we will collect DNA samples from a broad range of individuals belonging to one of the following groups: a) veterans who experienced mild to moderate traumatic brain injury (TBI) and are experiencing current major depressive disorder (+TBI/ +MDD), b) veterans who experienced mild to moderate TBI and are not experiencing current MDD (+TBI/ -MDD), c) veterans who have not experienced TBI and are experiencing current MDD (-TBI/ +MDD), d) veterans who have not experienced TBI and are not experiencing current MDD (-TBI/ -MDD), e) individuals (veterans and non-veterans) with a chronic pain disorder and/or a mood disorder, f) individuals (veterans and non-veterans) with no history of a chronic pain or mood disorder. Diagnostic information will come from a review of prior research records from studies within our group. Genotypes will be obtained for these individuals at loci where there is either known or suspected physiological variation. Genotypes will also be obtained for other genetic loci, but when there is no known or suspected relationship to physiology, these data will be used only for establishing population allele frequencies.